Process integration studies on Kraft pulp-mill-based biorefineries producing ethanol

Large scale, sustainable production of biofuels will require commercialization ofprocesses using lignocellulosic feedstocks. These processes are still notcompetitive with existing pathways, however. The competitiveness oflignocellulosic biofuel production plants could potentially be improved if theywere integrated with already existing facilities. One such example being exploredcurrently is connected to the fact that the pulping industry is showing a growinginterest in expanding their product portfolio, namely the complete or partialconversion of pulp mills into biorefineries for production of transport fuels.The objective of the work presented in this thesis has been to study differentpotential biorefinery concepts connected to chemical pulping, and morespecifically the Kraft pulping process. Three different process combinations havebeen assessed in the project; a process where a Kraft pulp mill is repurposed toethanol production (no pulp is produced), a process where ethanol and dimethyl-ether is produced in a repurposed Kraft pulp mill, and finally a processwhere an ethanol plant is co-located with a modern Kraft pulp mill.The findings from the studies reveal that an increasing degree of heat integrationleads to a lower production cost of ethanol both if the ethanol plant is based on arepurposed mill and if the plant is co-located with a modern mill. In the ethanolanddi-methyl-ether process, which has much higher conversion efficiency fromfeedstock to biofuel than the other processes, it was shown that the process couldbe competitive with the other combinations in terms of production cost, if thebiofuel price is high and if the biorefinery is perceived as a low risk investment